This invention relates to systems for monitoring a perimeter of an area and for reliably sounding an alarm in response to ingress or egress across the perimeter.
As an introduction to the problems solved by the present invention, consider for example the conventional perimeter alarm system based on laser beam interruption as used to monitor ingress onto a swimming pool apron. Such a system is difficult to initially install and requires considerable maintenance to control the occurrence of false alarms.
Many different physical effects of the installation can independently effect a false alarm. For example, when infrared laser sources are used with several mirrors to create a continuous path around the perimeter to be monitored, the initial alignment of the laser sources and reflectors is costly. If any one source or mirror becomes misaligned, through sudden or gradual movement, the beam is interrupted as a false alarm. Correction of misalignment may require use of expensive infrared sensitive equipment. When the several mirrors are aligned sufficiently to remove the false alarm, one or more mirrors may not be positioned to reflect the beam from the center of the mirror. Consequently, the system""s tolerance for future misalignment may be lower than expected.
The conventional detector for such a system may raise false alarms in response to light from sources other than from the laser source. Ambient sunlight may impinge upon the detector directly or as reflected by any surrounding surface or mirror. The angle of direct sunlight varies throughout the day and throughout the year to include a very wide range of angles. In addition, sunlight reflects from the surface of water in the swimming pool in an even wider range of angles varying randomly with wind conditions. The amount of background light on which a change is to be detected also varies making false detection more likely. An alignment of mirrors prescribed during installation or maintenance is unlikely to be sufficient for all of the above conditions.
The operator of such a system is exposed to risk of loss unnecessarily and possible responsibility for injury. As a result of false alarms, operators of such perimeter monitoring systems may be less likely to respond immediately when an alarm sounds. Failure to timely respond may result in a loss of life or property. When interrupted by a large number of false alarms, the operator may defeat the monitor or the alarm and not reactivate the monitor or the alarm due to operator irresponsibility or forgetfulness.
In view of the problems described above, the need remains in perimeter monitoring systems for higher reliability, greater safety, and lower installation and maintenance costs.
A perimeter monitoring system according to various aspects of the present invention includes a first and a second mounting apparatus, a reflector assembly, and a monitor. Each mounting apparatus includes a tube having an axial interior slot, and a pivot. The reflector assembly is positioned to receive a beam of light along a segment of a perimeter of an area to be monitored and to provide a returned beam. The reflector assembly includes a reflector secured to the pivot of the first mounting apparatus. The monitor includes an enclosure, an alarm controller, and a circuit board which includes an emitter and a detector. The emitter provides the beam of light. The detector provides a signal when an interruption of the returned beam is detected. The circuit board is mounted in the slot of the second mounting apparatus. The pivot of the second mounting apparatus is secured to the enclosure. The alarm controller activates an alarm in response to the signal.
By using a dual purpose mounting apparatus for the circuit board and for the reflector, installation is simplified and manufacturing costs are reduced. Initial set up and maintenance of such a system are greatly simplified by the use of visible light, use of a retroreflector, use of a dual purpose mounting apparatus and the combination of these features. Placement of reflectors in cooperation with the retroreflector is also simplified. The result is a much wider tolerance for misalignment of such reflectors and of the retroreflector, and consequently, a dramatic decrease in installation and maintenance costs.
According to various aspects of the present invention, a perimeter monitoring system includes: a reflector, a monitor, and a receiver. The reflector is positioned to receive a beam of light along a segment of a perimeter of an area to be monitored and to provide a returned beam. The monitor includes an emitter, a detector, an alarm, and a controller. The emitter provides the beam of light. The detector provides a first signal when an interruption of the returned beam is detected. The controller includes a timer that, when activated, reverts to being inactive after lapse of a period of time. The controller activates the alarm to provide a first warning when the timer is active and a second warning in response to the first signal when the timer is inactive. The controller activates the timer in response to a second signal provided by the receiver.
Use of such a system avoids periods without monitoring when an owner fails to reactivate the alarm after disabling the alarm. For example, when the timer is active, the first warning (e.g. a brief audible chirp) serves as a reminder that the first warning is disabled. When the timer has lapsed, the first warning is enabled, restoring monitoring with the second warning (e.g. a loud continuous tone).
In a variation, when an interruption of the returned beam is detected, the emitter is disabled for a period of time and then restarted.
In still another system according to various aspects of the present invention, a perimeter monitoring system includes: a reflector, a remote alarm, and a monitor. The reflector is positioned to receive a beam of light along a segment of a perimeter of an area to be monitored and to provide a returned beam. The remote alarm includes a remote transmitter that transmits a status signal and a remote receiver that receives an alert signal and activates a first alarm in response to the alert signal. The monitor includes an emitter, a detector, a second alarm, a transmitter, a receiver, and a controller. The emitter provides the beam of light. The detector provides a first signal when an interruption of the returned beam is detected. The transmitter transmits the alert signal in response to the first signal. The receiver provides a second signal in response to receiving the status signal. The controller includes a timer that provides a third signal in response to absence of the second signal for a period of time. The controller activates the second alarm to provide a first warning in response to the first signal when the timer is active, and activates the second alarm to provide a second warning in response to the third signal.
In addition to monitoring the perimeter, a system of the type described above makes known a condition wherein the remote alarm is not enabled. Such a condition includes, for example, silencing the remote alarm, loss of power to the remote alarm, and failure of the remote alarm.